🚀 perf: make render-cache compression opt-in, default off

.env.example

@@ -31,6 +31,9 @@ MAX_TERMINAL_CELLS=256000
 
 # Memory budget in MB for the rendered-frame cache (0 disables caching).
 RENDER_CACHE_MB=256
+# Compress cached frames (flate). Cuts cache RAM ~2x but decompresses on every
+# cache hit, so CPU rises with concurrent sessions. Off = zero-copy reads.
+RENDER_CACHE_COMPRESS=false
 
 # Go soft memory limit; set below your container limit to avoid OOM kills.
 GOMEMLIMIT=1GiB